In the copending patent application of E. J. Torok, et al., Ser. No. 603,840, having a filing date of Aug. 11, 1975, there is disclosed an optical page composer that is comprised of a magnetizable film layer in which single wall domains or bubbles may be sustained and moved about and to which are inductively coupled a digit line and a perpendicular word line, the intersection of which forms four quadrants that define or are defined by a memory area in the layer. An opaque shield is oriented in the memory area for optically shielding a bubble except when in the first quadrant within the memory area. Coincident current selection, e.g., concurrent half-current selection, of the digit line and of the word line by half-select write signals of the proper polarities permits the one fully selected memory area to be fully selected for the selective writing of a 1 or of a 0 therein, i.e., the associated bubble is selectively positioned in either the first or the third quadrant.
The optical page composer is preferably comprised of a magnetizable film layer of, e.g., garnet, having orthogonal sets of parallel digit lines and parallel word lines, each intersection of which forms four quadrants that define or are defined by an associated memory area with an opaque shield oriented in three of the four quadrants of each memory area. Coincident current selection of a selected one of the digit lines and of a selected one of the word lines by half-select write signals of a first polarity for the writing of a 1 and of a second and opposite polarity for the writing of a 0 permits each separate one of the memory areas to be separately selected for the selective positioning of the associated bubble in either the first quadrant (write 1) or the third quadrant (write 0) of the associated memory area without substantially affecting the bubbles in the half-selected memory areas along the half-selected digit line and word line.
In the operation of such page composer, as during the writing or transferring operation, it has been observed that the bubbles, under certain operating conditions, may escape from their proper stable positions, e.g., the first quadrant, within the memory area, or, alternatively, may become "struck" in one stable position and may not be selectively positioned from one stable position, e.g., the first quadrant, into another stable position, e.g., the third quadrant. The present invention is directed toward a method of ensuring the reliable operation of the page composer of such E. J. Torok, et al., patent application without a modification of the stripline structure thereof, except for a predetermined stripline-magnetic film layer separation.